India has denied claims that it has exported large quantities of counterfeit medication to Africa, after the Guardian published a front-page exposé on the phenomenon.

"No fake medicines have been sent from India to the continent of Africa," a spokesman for the ministry of external affairs in Delhi said.

The article cited experts and NGO reports as saying that up to a third of anti-malarial drugs in Uganda and Tanzania might be fake or substandard, and the majority of them were manufactured in China and India. The drugs look identical to real ones, and can only be distinguished with lab testing.

Aside from malaria drugs, analysis of antibiotics and contraceptives has also identified fakes. "Some pills contain no active ingredients, some are partial strength and some the wrong formulation entirely," said the article.

The fake medications have led to deaths, prolonged illness and increased drug resistance in parts of east Africa, the article said.

The Indian official said allegations of the nature of those mentioned in the Guardian had "surfaced previously" and "had been thoroughly investigated both in Africa and in India and found to be baseless".

"As the Guardian report acknowledges, India has stepped up oversight on this subject [and] ... continues to interact extensively with countries in Africa to provide quality medicines at affordable prices," the spokesman said.

"The government of India is committed to continue this co-operation in the strong belief that this is an ideal means of enhancing south-south co-operation and engagement."

Counterfeit drugs are a long-running issue in China. According to official statements, Chinese police seized £113m of fake pharmaceuticals in July alone and £19m worth in November. Many ingredients were found to be harmful or toxic.

The Indian health ministry launched a huge campaign last month to check the quality of medication manufactured across the country. India is home to more than 10,000 drug manufacturers.